Door securing or latching means for truck and trailer cargo doors are typically of two types. In one type, commonly used with swinging-type doors, a rod having latch lugs at its ends is mounted on a door and when the door is to be secured, the rod is rotated by a latch handle means attached thereto, so as to cause the latch lugs to engage corresponding catches on the truck or trailer body. In another type, commonly used with roll-up doors, a pivoted latch handle mounted near the bottom of the door has a latch hook opposite its handle portion. When this type of door is to be secured, the latch handle is rotated about its pivot so as to cause the latch hook to engage a catch carried in the truck or trailer body. In both types of closures, the latching action employed is commonly overcenter, and the door will remain latched until the latch handle is manually moved to an unlatching position.
In order to prevent unauthorized access to the cargo area, the door latch may typically be provided with means for securing the latch handle to prevent its movement to an unlatching position. Commonly utilized latch handle securing means may typically include a staple tab or ear on the latch handle which aligns with a corresponding stable tab mounted on the door when the latch handle is in a latched position, so that the shackle of a padlock may be passed through the aligned staple tabs to secure the latch handle in its latching position. In another approach, utilized for double swinging-door trailers, staple tabs are mounted to the latch rod of each door, so that when the doors are latched, the staple tabs on each door's latch rod are brought into adjacent alignment permitting a padlock shackle to be passed therethrough to prevent the rods being rotated to an unlatching position.
Such door latch securing means have a number of disadvantages. The staple tabs are typically neither robustly mounted nor of robust construction. The latch handle, being a lever, provides a means for an unauthorized user to apply considerable force upon the latch using the latch handle as a means of grasping or permitting the application of tools to break the staple tab. It is well known, for example, to slip a pipe over the end of a latch handle to obtain great leverage and thereby, to apply so much force that the staple tabs may be broken off. Alternatively, a prybar may be used to pry a staple tab loose from its mounting, or a chisel may be used to cut a staple tab off.
The padlock used to secure the door latch is also vulnerable to tampering. It is well known, for example, to use bolt cutting tools, saws and even cutting torches to cut through the shackle of a padlock, thus permitting its removal.
Freight shipments of goods and equipment may often be valued in millions of dollars and it thus becomes desirable to provide means for effectively securing cargo compartments against unauthorized access which overcome the disadvantages of known locking means and which resist attempted tampering.